Conventional articles of footwear generally include two primary elements: an upper and a sole structure. The upper is secured to the sole structure and forms a cavity for comfortably and securely receiving a foot. The sole structure is secured to a lower area of the upper, thereby being positioned between the upper and the ground.
In some embodiments, the sole structure includes a midsole and an outsole. The midsole often includes a polymeric foam material that attenuates ground reaction forces to lessen stresses upon the foot and leg during walking, running, and other ambulatory activities. Additionally, the midsole may include fluid-filled chambers, plates, moderators, or other elements that further attenuate forces, enhance stability, or influence the motions of the foot. The outsole is secured to a lower surface of the midsole and provides a ground-engaging portion of the sole structure formed from a durable and wear-resistant material, such as rubber.
The upper can generally extend over the instep and toe areas of the foot, along the medial and lateral sides of the foot and around the heel area of the foot. In some articles of footwear, the upper may extend upward and around the ankle to provide support or protection for the ankle. Access to the cavity within the upper is generally provided by an ankle opening in a heel region of the footwear.
Additionally, the article of footwear can include a lacing system, cables, straps, buckles, or other securement device. The securement device can adjust the fit of the upper, thereby permitting entry and removal of the foot from the upper. The lacing system also permits the wearer to modify certain dimensions of the upper, particularly girth, to accommodate feet with varying dimensions.